1. Field of the Invention
The present invention relates to a tunneling magnetoresistive element mounted on a magnetic reproducing apparatus, for example, a hard disk device, or the like, or another magnetic sensing device. Particularly, the present invention relates to a tunneling magnetoresistive element which can stably produce a rate of change in resistance, and which can be formed with high reproducibility, and a method of manufacturing the same.
2. Description of the Related Art
FIG. 21 is a partial sectional view illustrating the structure of a conventional tunneling magnetoresistive element.
In FIG. 21, reference numeral 1 denotes an electrode layer made of, for example, Cu, W, Cr or the like.
An antiferromagnetic layer 2, a pinned magnetic layer 3, an insulating barrier layer 4 and a free magnetic layer 5 are laminated in turn to form a multilayer film 6 on the electrode layer 1.
The antiferromagnetic layer 2 is made of an existing antiferromagnetic material such as a NiMn alloy film or the like, and heat treatment of the antiferromagnetic layer 2 produces an exchange coupling magnetic field between the pinned magnetic layer 3 made of a ferromagnetic material such as a NiFe alloy film or the like and the antiferromagnetic layer 2 to pin the magnetization direction of the pinned magnetic layer 3 in the Y direction (height direction) shown in FIG. 21.
The insulating barrier layer 4 is made of an existing insulating material such as Al2O3 or the like, and the free magnetic layer is made of the same material as the pinned magnetic layer 3, such as a NiFe alloy film or the like.
Referring to FIG. 21, bias layers 9 made of a hard magnetic material such as a Coxe2x80x94Pt alloy film or the like are formed on both sides of the multilayer film 6 in the track width direction (the X direction shown in the drawing).
The bias layers 9 supply a bias magnetic field to the free magnetic layer 5 in the X direction shown in the drawing to orient the magnetization direction of the free magnetic layer 5 in the X direction.
As shown in FIG. 21, an electrode layer 10 is formed on the multilayer film 6 and the bias layers 9.
The tunneling magnetoresistive element serves as a reproducing magnetic element utilizing a tunneling effect for detecting a leakage magnetic field from a recording medium. When a sensing current is supplied to the multilayer film 6 from the electrode layers 1 and 10 in the Z direction shown in the drawing, a tunneling current changes based on the magnetization relation between the free magnetic layer 5 and the pinned magnetic layer 3 to cause a change in resistance, thereby detecting a recording signal by the change in resistance.
However, the structure of the tunneling magnetoresistive element shown in FIG. 21 has the following problem.
Since the sensing current supplied from the electrode layers 1 and 10 flows not only through the multilayer film 6 but also through the bias layers 9 formed on both sides of the multilayer film 6 to fail to obtain a TMR effect, thereby significantly deteriorating the function and properties of the reproducing magnetic element.
FIG. 22 shows another tunneling magnetoresistive element having a structure which is improved for resolving the above problem.
Referring to FIG. 22, insulating layers 7 made of, for example, Al2O3 or the like, are formed on both sides of the multilayer film 6 in the track width direction (the X direction shown in the drawing).
By forming the insulating layers 7, a plane surface extends on the same plane as the upper surface of the multilayer film 6, the bias layers 9 made of a hard magnetic material such as a Coxe2x80x94Pt film being respectively formed on the insulating layers 7 with underlying layers 8 of Cr provided therebetween.
Each of the hard magnetic bias layers 9 is formed to further extend from the insulating layer 7 to the upper surface of the multilayer film 6 by a width dimension T1. As a result, the magnetization direction of the free magnetic layer is oriented in the X direction by a bias magnetic field from the bias layers 9.
In the structure shown in FIG. 22, the insulating layers 7 are formed on both sides of the multilayer film 6, and thus the sensing current from the electrode layers 1 and 10 appropriately flows through the multilayer film 6 with less shunt current. Also, in this structure, the bias magnetic field from the bias layers 9 flows into the free magnetic layer 5 from the top thereof, not from the sides of the free magnetic layer 5.
However, the tunneling magnetoresistive element shown in FIG. 22 has the following problem.
As shown in FIG. 22, a bias magnetic field A from the bias layers 9 is oriented in the track width direction (the X direction shown in the drawing) to supply a magnetic field to the free magnetic layer 5 in the X direction. However, at the same time, a magnetic field B oriented in the direction opposite to the bias magnetic field A occurs in the portion of the free magnetic layer 5 which contacts of the extension of each of the bias layers 9 on the multilayer film 6. The occurrence of the magnetic field B destabilizes the magnetic domain structure of the free magnetic layer 5 to cause the occurrence of Barkhousen noise or destabilize a reproduced waveform, thereby deteriorating reproducing characteristics.
As described below, the structure of the magnetic element shown in FIG. 22 causes difficulties in forming the bias layers 9 with high alignment accuracy, causing variations in the width dimension T1 of the extension of each of the bias layers 9. Particularly, the bias layers 9 are formed to extend on a sensitive zone of the multilayer film 6, which substantially exhibits a magnetoresistive effect, and thus the magnetic domain structure of the sensitive zone is significantly destabilized due to the occurrence of the magnetic field B. Also, the extensions of the bias layers 9 to the sensitive region significantly decrease a zone which can exhibit the magnetoresistive effect, thereby deteriorating characteristics.
The occurrence of the magnetic field B is due to the formation of the underlying layers 8 made of Cr between the free magnetic layer 5 and the bias layers 9. The presence of the underlying layers 8 interrupts magnetic coupling between the free magnetic layer 5 and the bias layers 9.
There is thus the idea that the underlying layers 8 are removed to directly joint the free magnetic layer 5 and the bias layers 9. However, without the underlying layers 8, the coercive force of the bias layers 9 cannot be ensured to cause difficulties in controlling crystal orientation, thereby significantly deteriorating hard magnetic properties.
The method of manufacturing the tunneling magnetoresistive element shown in FIG. 22 also has the following problems.
As shown in FIG. 23, after the electrode layer 1, the multilayer film 6 and the insulating layers 7 are formed, the bias layer 9 is formed on the multilayer film 6 and the insulating layers 7.
In FIG. 24, a resist layer 11 is formed on the bias layer 9, and then exposed and developed to form an aperture pattern 11a having a predetermined with dimension in the central portion of the resist layer 11. Then, the bias layer 9 exposed from the aperture pattern 11a is removed by etching to form the bias layers 9 having the shape shown in FIG. 9.
However, it is difficult to form the aperture pattern 11a with high precision at a predetermined portion of the resist layer 11 at the top of the multilayer film 6, which has a very small width dimension, thereby causing variations in the shape of the bias layers 9 to deteriorate reproducibility.
Furthermore, in the step of etching the bias layers 9 exposed from the aperture pattern 11a, a portion of the free magnetic layer 5 below the bias layer 9 is also possibly removed to make it difficult to control the etching time or the like. Since the free magnetic layer 5 is formed to a small thickness of several tens nm, a variation occurs in the properties even when only a small amount of the free magnetic layer 5 is removed.
Also, the structure of the tunneling magnetoresistive element shown in FIG. 22 easily produces a variation in a reproducing gap. As shown in FIG. 22, the length from the lower electrode layer 1 to the upper electrode layer 10 is h1 in the central portion where the bias layers 9 are not formed on the multilayer film 6, while the length is h2 in the portion where the bias layers 9 are formed on the multilayer film 6, the length h2 being longer than the length h1. Therefore, a variation occurs in the thickness of the reproducing gap within the width dimension of the multilayer film 6 in the track width direction (the X direction shown in the drawing), easily causing an adverse effect on the reproducing characteristics.
The present invention has been achieved for solving the above problems of a conventional element, and an object of the present invention is to provide a tunneling magnetoresistive element permitting appropriate supply of a bias magnetic field to a free magnetic layer to stabilize a reproduced waveform, and a method of manufacturing the tunneling magnetoresistive element exhibiting high reproducibility of formation.
In an aspect of the present invention, there is provided a tunneling magnetoresistive element comprising a multilayer film comprising an antiferromagnetic layer, a pinned magnetic layer formed in contact with the antiferromagnetic layer so that the magnetization direction is pinned by an exchange coupling magnetic field with the antiferromagnetic layer, and a free magnetic layer formed on the pined magnetic layer with an insulating barrier layer provided therebetween, electrode layers formed above and below the multilayer film, insulating layers formed on both sides of the multilayer film in the track width direction, and domain control layers respectively formed on the insulating layers so as to contact at least portions of both side surfaces of the free magnetic layer, for orienting the magnetization direction of the free magnetic layer in a direction crossing the magnetization direction of the pinned magnetic layer, wherein the domain control layers are formed so as not to extend to the upper surface of the multilayer film.
In the present invention, the antiferromagnetic layer, the pinned magnetic layer, the insulating barrier layer and the free magnetic layer are formed in turn from the bottom to form the multilayer film, and the insulating layers and the domain control layers are formed on both sides of the multilayer film.
The domain control layers are formed in contact with at least portions of both sides surfaces of the free magnetic layer so as not to extend to the upper surface of the multilayer film.
By providing the insulating layers on both sides of the multilayer film, as described above, a sensing current from the electrode layers appropriately flows through the multilayer film to decrease a shunt loss of the sensing current, thereby improving reproduced output.
Since the domain control layers are formed in contact with both side surfaces of the free magnetic layer, a bias magnetic field from the domain control layers is appropriately supplied to the free magnetic layer through the sides thereof, permitting magnetization control of the free magnetic layer.
Furthermore, unlike in the conventional example shown in FIG. 22, the domain control layers are formed so as not to extend to the upper surface of the multilayer film, and thus the reverse magnetization field B does not occur in the free magnetic layer, thereby stabilizing the magnetic domain structure of the free magnetic layer. More specifically, the free magnetic layer can be appropriately put into a single magnetic domain structure state.
In another aspect of the present invention, there is provided a tunneling magnetoresistive element comprising a multilayer film comprising an antiferromagnetic layer, a pinned magnetic layer formed in contact with the antiferromagnetic layer so that the magnetization direction is pinned by an exchange coupling magnetic field with the antiferromagnetic layer, a free magnetic layer formed on the pined magnetic layer with an insulating barrier layer provided therebetween, electrode layers formed above and below the multilayer film, insulating layers formed on both sides of the multilayer film in the track width direction, and domain control layers formed on the insulating layers so as to contact at least portions of both side surfaces of the free magnetic layer, for orienting the magnetization direction of the free magnetic layer in a direction crossing the magnetization direction of the pinned magnetic layer, wherein the multilayer film comprises a central sensitive zone having excellent reproducing sensitivity so that a magnetoresistive effect can be substantially exhibited, and dead zones formed on both sides of the sensitive zone and having low reproducing sensitivity so that the magnetoresistive effect cannot be substantially exhibited, and the domain control layers are formed so as to extend on the multilayer film.
In the present invention, the domain control layers are formed to extend on the multilayer film, but extend only on the dead zones of the multilayer film.
In the multilayer film, not the entire region exhibits the magnetoresistive effect, but only the central area has excellent reproducing sensitivity and can substantially exhibit the magnetoresistive effect. The area having excellent reproducing sensitivity is referred to as a xe2x80x9csensitive zonexe2x80x9d, and the areas on both sides of the sensitive zone, which have poor reproducing sensitivity, are referred to as xe2x80x9cdead zonesxe2x80x9d. The sensitive zone and the dead zones in the multilayer film are measured by, for example, a micro-track profile method.
In the present invention, the domain control layers may be formed to extend on the dead zones. Even when as in a conventional element, underlying layers are interposed between the domain control layers and the multilayer film, for controlling the crystal orientation of the domain control layers, a reverse magnetic field (refer to reference character B shown in FIG. 22) occurring in the free magnetic layer is produced only in the dead zones thereof, thereby causing no adverse effect on the reproducing characteristics.
Furthermore, the domain control layers are formed on the dead zones, not formed on the sensitive zone, and thus the reproducing gap within the sensitive zone has a uniform thickness, causing no fear of deterioration in characteristics.
In a still another aspect of the present invention, there is provided a tunneling magnetoresistive element comprising a multilayer film comprising a free magnetic layer, a pinned magnetic layer formed on the free magnetic layer with an insulating barrier layer provided therebetween, and an antiferromagnetic layer formed on the pinned magnetic layer, for pinning the magnetization direction of the pinned magnetic layer by an exchange coupling magnetic field, electrode layers formed above and below the multilayer film, domain control layers formed on both sides of the multilayer film in the track width direction so as to contact at least portions of both side surfaces of the free magnetic layer, for orienting the magnetization direction of the free magnetic layer in a direction crossing the magnetization direction of the pinned magnetic layer, and insulating layers respectively formed on the domain control layers, wherein the insulating layers are formed so as not to extend to the upper surface of the multilayer film.
In the present invention, the free magnetic layer, the insulating barrier layer, the pinned magnetic layer and the antiferromagnetic layer are laminated in turn from the bottom to form the multilayer film.
Since the domain control layers are formed to contact at least portions of both side surfaces of the free magnetic layer, a bias magnetic field can be appropriately supplied to the free magnetic layer from the domain control layers.
Also, the insulating layers are formed on the domain control layers, and thus a sensing current from the electrode layers appropriately flows through the multilayer film to decrease a shunt loss of the sensing current, thereby permitting an attempt to improve reproduced output.
Since the insulating layers are formed so as not to extend to the upper surface of the multilayer film, no variation occurs in the thickness of the reproducing gap within the width dimension of the multilayer film in the track width direction, thereby causing no fear of deteriorating characteristics.
In a further aspect of the present invention, there is provided a tunneling magnetoresistive element comprising a multilayer film comprising a free magnetic layer, a pinned magnetic layer formed on the free magnetic layer with an insulating barrier layer provided therebetween, and an antiferromagnetic layer formed on the pinned magnetic layer, for pinning the magnetization direction of the pinned magnetic layer by an exchange coupling magnetic field, electrode layers formed above and below the multilayer film, domain control layers formed on both sides of the multilayer film in the track width direction so as to contact at least portions of both side surfaces of the free magnetic layer, for orienting the magnetization direction of the free magnetic layer in a direction crossing the magnetization direction of the pinned magnetic layer, and insulating layers formed on the domain control layers, wherein the multilayer film comprises a central sensitive zone having excellent reproducing sensitivity so that the magnetoresistive effect can be substantially exhibited, and dead zones formed on both sides of the sensitive zone and having poor reproducing sensitivity so that the magnetoresistive effect cannot be substantially exhibited, and the insulating layers are formed so as to extend on the dead zones of the multilayer film.
In the present invention, the insulating layers are formed to extend on the dead zones of the multilayer film, not on the sensitive zone thereof, and thus no variation occurs in the thickness of the reproducing gap within the sensitive zone, causing no fear of deteriorating characteristics.
In the present invention, underlying layers are preferably formed below the domain control layer, for controlling the crystal orientation of the domain control layers. This can sufficiently maintain the magnetic properties of the domain control layer.
In the present invention, with the domain control layers formed to extend on the dead zones of the multilayer film, a magnetic filed in the direction opposite to the bias magnetic field of the domain control layers occurs in the multilayer film due to the presence of the underlying layers. However, the reverse magnetic field occurs within the dead zones, and thus the reproducing characteristics are not adversely affected.
Each of the domain control layers preferably comprises a hard magnetic material.
In the present invention, each of the domain control layers may comprise a laminated film of a ferromagnetic layer and a second antiferromagnetic layer, the ferromagnetic layers being in contact with at least portions of both side surfaces of the free magnetic layer.
In the present invention, the insulating layers may comprise an antiferromagnetic insulating layer exhibiting an antiferromagnetic property, and the domain control layers may comprise a ferromagnetic layer.
In this case, the second antiferromagnetic layer or the antiferromagnetic layer is preferably made of xcex1-Fe2O3.
A method of manufacturing a tunneling magnetoresistive element of the present invention comprises:
(a) the step of forming an electrode layer on a substrate, and then laminating an antiferromagnetic layer, a pinned magnetic layer in which magnetization is pinned in a predetermined direction by an exchange coupling magnetic field with the antiferromagnetic layer, an insulating barrier layer and a free magnetic layer in turn from the bottom to form a multilayer film;
(b) the step of forming, on the multilayer film, a lift-off resist layer having notched portions formed on the lower side thereof;
(c) the step of removing both sides of the mulitlayer film leaving at least a portion of the multilayer film below the resist layer;
(d) the step of forming insulating layers on both sides of the multilayer film so that the multilayer film-side ends of the upper surfaces of the insulating layers are lower than both ends of the upper surface of the free magnetic layer;
(e) the step of forming domain control layers on the insulating layers by sputtering obliquely to the substrate so that the domain control layers contact both ends of the free magnetic layer, and the multilayer film-side ends of the upper surfaces of the domain control layers coincide with the both ends of the upper surface of the multilayer film; and
(f) the step of removing the resist layer, and forming an electrode layer on the multilayer film and the domain control layers.
In the present invention, as described above, the lift-off resist having notched portions formed on the lower side thereof is used for forming the insulating layers and the domain control layers on both sides of the multilayer film.
Therefore, unlike a conventional manufacturing method (refer to FIGS. 23 and 24), alignment precision for forming an aperture pattern in a resist layer is unnecessary, and thus less variation occurs in the shape of the domain control layers as compared with the conventional method. Therefore, a tunneling magnetoresistive element can be manufactured with high reproducibility.
In the above-described manufacturing method, the domain control layers can be formed in contact with both side surfaces of the free magnetic layer so as not to extend to the upper surface of the multilayer film.
Another method of manufacturing a tunneling magnetoresistive element of the present invention comprises:
(a) the step of forming an electrode layer on a substrate, and then laminating an antiferromagnetic layer, a pinned magnetic layer in which magnetization is pinned in a predetermined direction by an exchange coupling magnetic field with the antiferromagnetic layer, an insulating barrier layer and a free magnetic layer in turn from the bottom to form a multilayer film;
(b) the step of forming, on a sensitive zone of the multilayer film, a lift-off resist layer having notched portions formed on the lower side thereof;
(c) the step of removing both sides of the mulitlayer film leaving at least a portion of the multilayer film below the resist layer;
(d) the step of forming insulating layers on both sides of the multilayer film so that the multilayer film-side ends of the upper surfaces of the insulating layers are lower than both ends of the upper surface of the free magnetic layer;
(e) the step of forming domain control layers on the insulating layers by sputtering obliquely to the substrate so that the domain control layers contact both ends of the free magnetic layer, and extend on dead zones of the multilayer film; and
(f) the step of removing the resist layer, and forming an electrode layer on the multilayer film and the domain control layers.
This manufacturing method is capable of manufacturing a tunneling magnetoresistive element with high reproducibility, and forming the domain control layers to extend only on the dead zones of the multilayer film.
Another method of manufacturing a tunneling magnetoresistive element of the present invention comprises:
(a) the step of forming an electrode layer on a substrate, and then laminating a free magnetic layer, an insulating barrier layer, a pinned magnetic layer, and an antiferromagnetic layer for pinning magnetization of the pinned magnetic layer in a predetermined direction by an exchange coupling magnetic field in turn from the bottom to form a multilayer film;
(b) the step of forming, on the multilayer film, a lift-off resist layer having notched portions formed on the lower side thereof;
(c) the step of removing both sides of the multilayer film leaving a portion of the multilayer film below the resist layer;
(d) the step of forming domain control layers on both sides of the multilayer film so that the multilayer film-side ends contact at least portions of both ends of the free magnetic layer;
(e) the step of forming insulating layers on the domain control layers by sputtering obliquely to the multilayer film so that the multilayer film-side ends of the upper surfaces of the insulating layers coincide with both ends of the upper surface of the multilayer film; and
(f) the step of removing the resist layer, and forming an electrode layer on the multilayer film and the insulating layers.
In this case, the free magnetic layer, the insulating barrier layer, the pinned magnetic layer and the antiferromagnetic layer are laminated in turn from the bottom to form the multilayer film. In addition, the domain control layers and the insulating layers are formed on both sides of the multilayer film by using the lift-off resist layer to cause less variation in the shapes of the domain control layers and the insulating layers, thereby permitting the manufacture of a tunneling magnetoresistive element with high reproducibility.
In the present invention, the insulating layers may be formed so as not to extend to the upper surface the multilayer film.
Another method of manufacturing a tunneling magnetoresistive element of the present invention comprises:
(a) the step of forming an electrode layer on a substrate, and then laminating a free magnetic layer, an insulating barrier layer, a pinned magnetic layer, and an antiferromagnetic layer for pinning magnetization of the pinned magnetic layer in a predetermined direction by an exchange coupling magnetic field in turn from the bottom to form a multilayer film;
(b) the step of forming, on a sensitive zone of the multilayer film, a lift-off resist layer having notched portions formed on the lower side thereof;
(c) the step of removing both sides of the multilayer film leaving at least a portion of the multilayer film below the resist layer;
(d) the step of forming domain control layers on both sides of the multilayer film so that the multilayer film-side ends contact at least portions of both ends of the free magnetic layer;
(e) the step of forming insulating layers on the domain control layers by sputtering obliquely to the multilayer film so that the insulating layers extend on dead zones of the multilayer film; and
(f) the step of removing the resist layer, and forming an electrode layer on the multilayer film and the insulating layers.
In this case, a tunneling magnetoresistive element can be manufactured with high reproducibility. Also, the insulating layers can be formed to extend only on the dead zones of the multilayer film.
In the present invention, underlying layers are preferably formed below the domain control layers, for controlling crystal orientation of the domain control layers. The underlying layers can be formed in the same step as the insulating layers and the domain control layers.
In the present invention, in the step (d), (j), (p) or (v), the insulating layers or the domain control layers are preferably formed by sputtering vertically to the substrate.
In the present invention, each of the domain control layers preferably comprises a hard magnetic material or a laminated film of a ferromagnetic layer and a second antiferromagnetic layer, the ferromagnetic layers being brought into contact with at least portions of both side surfaces of the free magnetic layer.
In the present invention, each of the insulating layers may comprise an antiferromagnetic insulating layer exhibiting antiferromagnetism, and each of the domain control layers may comprise a ferromagnetic layer.
In the present invention, the second antiferromagnetic layer or the antiferromagnetic insulating layer exhibiting antiferromagnetism may be made of xcex1-Fe2O3.